Nitrogen forms and the mitigation of cadmium toxicity in tanzania guinea grass

• Ano de defesa: 2019
• Autor(a) principal: Leite, Tiago de Sousa
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Panicum maximum; Adubação nitrogenada; Ammonium; Amônio; Antioxidant enzymes; Atividade fotossintética; Enzimas antioxidantes; Fitoextração; Metabolismo do nitrogênio; Nitrate; Nitrato; Nitrogen fertilization; Nitrogen metabolism; Photosynthetic activity; Phytoextraction
• Link de acesso: http://www.teses.usp.br/teses/disponiveis/11/11140/tde-02042019-145159/

Adequate nutrition plays a key role in the phytoextraction of soil contaminants and may influence the response of plants to heavy metal toxicity. Nevertheless, there is no information on the influence of nitrogen (N), particularly in the forms of nitrate (NO3-) and ammonium (NH4+), on tanzania guinea grass (Panicum maximum cv. Tanzania) under cadmium (Cd) stress. Thus, in the present work, it was aimed to study the effect of these ions on the mitigation of Cd toxicity in this grass. Plants were grown in a greenhouse, using plastic pots containing nutrient solution and ground quartz as substrate. The experiment was laid out in a randomized complete block design, in a 3 × 3 factorial arrangement, with six replications. The factors tested were NO3-/NH4+ ratios (100/0, 70/30 and 50/50) and Cd rates (0.0, 0.5 and 1.0 mmol L-1). Morphological, physiological and biochemical changes in the plants were studied throughout two growth periods. In addition to causing oxidative stress and visual toxicity symptoms, Cd exposure resulted in reduced chlorophyll content and photosynthetic activity, negatively affecting shoot and root growth. Moreover, it altered N metabolism and induced the accumulation of NO3- and NH4+ mainly in shoots, increasing plant total N concentration. The exclusive use of NO3- mitigated toxicity symptoms by favoring Cd accumulation in roots, maintaining normal N metabolism and increasing guaiacol peroxidase activity. On the other hand, although the simultaneous supply of NO3- and NH4+ increased the uptake, transport and accumulation of this metal by the grass, it also increased the photosynthetic capacity along with the synthesis of proline and protein. The use of these N forms at a 50/50 ratio increased the tolerance of the plants to Cd by inducing high superoxide dismutase and glutathione reductase activities in shoots and roots, respectively, maintaining cellular homeostasis and reducing oxidative stress. Cd uptake and accumulation in tanzania guinea grass are strongly related to the form of N available, and the negative effects of this metal on photosynthesis and on the balance between oxidants and antioxidants are attenuated by the partial replacement of NO3- by NH4+ in the nutrient solution.